Frequency layer convergence method for mbms

ABSTRACT

A method to control cell selection and/or re-selection in a communication system comprising a plurality of cells with which terminal devices may communicate, the method including the steps of: determining that a terminal device is to start a session for a certain service, the service using a reception frequency; based on that determination, changing at least one cell selection and/or re-selection parameter in respect of the terminal device with the effect that a subsequent cell selection and/or re-selection performed by the device would favor cells that use the reception frequency used in the service session over other cells.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U. S. patent application Ser. No.15/646,745, filed Jul. 11, 2017, which is a continuation of Ser. No.14/663,907, filed Mar. 20, 2015, now U.S. Pat. No. 9,736,657, which is acontinuation of Ser. No. 13/623,440, filed on Sep. 20, 2012, now U.S.Pat. No. 9,007.982, which is a continuation of U.S. patent applicationSer. No. 10/935,323, filed on Sep. 8, 2004, now U.S. Pat. No. 8,300,593,which is based upon and claims the benefit of priority from BritishPatent Application No. 0408568.4, filed Apr. 16, 2004, of which thecontents are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates primarily to a method for providing amultimedia broadcast multicast service (MBMS). In an embodiment of theinvention an MBMS is provided in a radio access network (RAN). However,it is envisaged that embodiments of the present invention may also beutilized in providing other types of service in a RAN. Specifically, thepresent invention may be implemented in a mobile telecommunicationsnetwork.

BACKGROUND OF THE INVENTION

A problem with implementing MBMS is that where there are cells ondifferent frequency layers, with a distribution of MBMS subscribersacross the different frequency layers, system capacity can be wasted ifthe same MBMS data stream is transmitted on the different frequencylayers to UEs in the same geographical coverage area. Examples includeoverlapping cells, whether co-located or not. The term “co-location” ingeneral is understood as cells on different frequencies have the samebase station site i.e. the transmission of two or more carrierfrequencies happens from the same base station site. However, inpractice the network may have two or more carrier frequencies, whichhave different cell sizes and therefore at least not all cells areco-located although the coverage of these these different frequencylayers are overlapping in a given geographical area. Hence, the problemdoes not only occur in co-located case but in all case and areas wherethe network has cell coverage on more than one frequency and therefore anetwork operator would like to provide MBMS service only on one of thecarrier frequencies (or at least not on all carrier frequencies)

3GPP TS 25.346 v6.0.0 discusses general structural and functionalaspects of providing MBMS in a RAN. Currently 25.346 v.6.0.0 definesfrequency layer convergence as follows:

“Frequency Layer Convergence denotes the process where the UTRANrequests UEs to preferentially re-select to the frequency layer on whichthe MBMS service is intended to be transmitted. This layer preferencecould be done by an additional MBMS session related Layer ConvergenceInformation (LCI) such as offset and target frequency. These kinds ofinformation could be given to UEs at session start and during the wholesession, and will be applied during the entire session. More than oneoffset may be required to support multiple frequencies, but it isassumed that the same LCI information will apply to all the services onthe same frequencies.”

R2-031716, 3GPP TSG RAN WG2 meeting #37 Budapest, Hungary, Aug. 25-29,2003 proposes frequency layer convergence (FLC) for MBMS.

R2-032077, TSG RAN WG2 meeting #38 Sophia Antipolis, France, Sep. 6-10,2003 discloses a UE layer convergence mechanism for MBMS.

R2-040086, TSG RAN WG2 meeting #38 Sophia Antipolis, France, Sep. 6-10,2003 discusses different alternatives for layer convergence and possibleMBMS frequency layer convergence procedures.

3GPP TS 25.346 v6.0.0 discusses general structural and functionalaspects of providing MBMS in a RAN. Currently 25.346 v.6.0.0 definesfrequency layer convergence as follows:

“Frequency Layer Convergence denotes the process where the UTRANrequests UEs to preferentially re-select to the frequency layer on whichthe MBMS service is intended to be transmitted. This layer preferencecould be done by an additional MBMS session related Layer ConvergenceInformation (LCI) such as offset and target frequency. These kinds ofinformation could be given to UEs at session start and during the wholesession, and will be applied during the entire session. More than oneoffset may be required to support multiple frequencies, but it isassumed that the same LCI information will apply to all the services onthe same frequencies.”

The intention behind the FLC concept is to maximise thepoint-to-multipoint (p-t-m) connections for an MBMS session, from theradio network controller (RNC) point of view. This is because MBMS inpoint-to-point (p-t-p) would not present many advantages over R99 DCHconnections since the same radio resources are consumed. Thus, FLCreduces system capacity wastage in that where there is overlapping cellcoverage on different frequency layers, with a distribution of MBMSsubscribers across the different frequency layers, the MBMS subscribersare moved onto the same frequency layer thereby negating the need totransmit the same MBMS data stream on multiple different frequencylayers to UEs in the same geographical coverage area.

The discussion in 25.346 v.6.0.0 and the proposals in documentsR2-031716, R2-032077 and R3-040086 do not define the details required toimplement a frequency layer convergence method for MBMS but insteaddiscuss generally the requirements for frequency layer convergence.

It is currently not possible to converge a UE to a certain cell orfrequency, which is different from the one that would be selected orreselected based on the normal cell reselection criteria in thefollowing radio resource control (RRC) states: Idle, CELL_PACH,CELL_PCH. Furthermore, it is also not possible to keep the UE on apreferred MBMS frequency layer when the cell reselection criteriaindicate a cell on another carrier frequency to be better and no thereis no cell barring.

SUMMARY OF THE INVENTION

It is an aim of the present invention o solve one or more of theabove-identified problems.

Aspects of the invention are set out in the claims.

According to an embodiment of the present invention not all MBMS capableUEs should reselect to the MBMS layer. Rather, only the UEs that startan MBMS session will move to the MBMS layer. This avoids all MBMS UEsreselecting always to the same frequency and minimizes the migrationtrend of MBMS UEs towards the same cells. For example, this featureprevents migration of MBMS UEs towards bigger cells in the case where amacro layer is the preferred MBMS layer and a micro layer is thepreferred normal HCS layer.

Preferably, the FLC feature is only applicable for MBMS capable UEs.However, it is envisaged that embodiments of the present invention mayalso be utilized in providing other types of service in a RAN.

Preferably, the FLC is active after notification. An MBMS notificationindicator channel (MICH) may be provided in the cells. Furthermore, anMBMS point-to-point traffic channel (MCCH) may also be provided in thecells. The MCCH that is sent on cells that are not on the preferred MBMSfrequency may not have all the data that is available in the MCCH senton the preferred MBMS laver. But the MCCH that is sent in cells that arenot on the preferred MBMS frequency contains the parameters needed forFLC. If the MCCH is not transmitted in cells together with MICH, thenthe FLC parameters should be (e.g.) broadcast in system information.This is less preferable.

Preferably, there is an explicit session stop to indicate disabling theFLC. The network is able to switch this feature ON/OFF, with thestart/finish of the MBMS session. The UE uses the FLC related cellreselection parameters and criteria during the MBMS session only (TheFLC is only available per MBMS session).

The changing step preferably comprises setting a parameter so as toencourage the terminal device to select or re-select a cell morepromptly. This may be done by triggering immediate selection orreselection or by altering a threshold so as to make selection orreselection more likely.

Embodiments of the invention preferably provide a solution for frequencylayer convergence for MBMS, which does not conflict with the existingcell reselection criteria and allows minimum changes to the cellreselection criteria. The invention introduces a solution for networks,with and without HCS (Hierarchical Cell Structure).

The network could send an FLC parameter upon notification.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample with reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram showing an embodiment of the presentinvention in a network having a hierarchical cell structure;

FIG. 2 is a schematic diagram showing an embodiment of the presentinvention in a network not having a hierarchical cell structure wherethe serving cell is not on the MBMS layer;

FIG. 3 is a schematic diagram showing an embodiment of the presentinvention in a network not having a hierarchical cell structure wherethe serving cell is on the MBMS layer;

FIG. 4 is a flow diagram illustrating the steps in an embodiment of themethod of the present invention;

FIG. 5 is an example of a possible session start sequence; and

FIG. 6 is an example of a possible session stop sequence.

FIG. 7 is an example of a MICH frame used in MBMS notification,

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 is shows a schematic diagram of a portion of a network having ahierarchical cell structure. The network comprises a macro-cell 2 and aplurality of micro-cells 4. The macro-cell comprises the MBMS layerwhile the micro-cells comprise the non-MBMS layer, Associated with thecells is a HCS priority represented by the parameter HCS_PRIO.Accordingly, a value for HCS_PRIO is associated with the MBMS layer anda value for HCS_PRIO is associated with the non-MBMS layer

Typically in a network using HCS, macro-cells have lower priority thanmicro-cells. That is, HCS_PRIO is different for each layer, and in FIG.1 HCS_PRIO is equal to 3 in the micro-cells and is equal to 2 in themacro-cell. Since the macro layer is the MBMS layer a change of priorityis required to reselect onto the MBMS layer for an MBMS session. Thatis, for networks using HCS, the HCS priority is modified by changingHCS_PRIO.

Hence, if a network uses HCS and HCS priorities are not aligned with theMBMS priorities, HCS_PRIO is changed for the MBMS layer uponnotification. This could be provided by means of frequencyidentification and an offset value to the parameter HCS_PRIO or anactual replacement value for HCS_PRIO. The FLC parameters may be sente.g. in the session control start message on MCCH or via SIB (SystemInformation Block types).

In FIG. 1 HCS_PRIO of the cell on the MBMS layer is changed from 2 to 4so as to have a higher HCS priority (HCS_PRIO) than the non-MBMS layer(for which HCS_PRIO is set at 3) for UEs that are notified to use theFLC. A change of priorities occurs after the notification. For other UEsHCS_PRIO remains unchanged. In this example the HCS_PRIO is changed from2 to 4, which means that the MBMS layer has higher priority for UEs thatare notified to use the FLC. For other UEs HCS_PRIO remains at 2. In thecase where the HCS priority and MBMS priority are the same in thenetwork no changes are required to the HCS priority. In this case thenetwork may either use FLC or decide to keep the normal cell reselectioncriteria for UEs that are notified about the start of a MBMS session.

When the MBMS session is finished, the priorities are changed back totheir original values and in the example shown in FIG. 1 the UE wouldreselect back to the micro-cell with a HCS_PRIO of 3.

The high mobility rules of the normal HCS priorities may not be validfor MBMS due to different prioritization. In this case the UE should notuse the existing HCS high mobility triggers and prioritization of lowerHCS priority layers when high mobility would be triggered based on thenormal HCS high mobility triggers defined in 25.346 v.6.0.0. This can beobtained either by explicitly defining in the specification that whenthe FLC is used, high mobility triggers and rules criteria should not beused or by a special signaling element that indicates whether highmobility triggers and criteria should be used in the FLC case as well.

The re-selection to the MBMS layer may either occur when the UE hasevaluated the H criterion of a cell in the MBMS layer to be higher than0 (H is defined in TS25.304) or immediately after the notification. Inthe case of the initial cell reselection initiated by the FLC, the UEmay disregard the penalty time and TEMP_OFFSET in order to allow fasterfrequency layer convergence. In the case where the UE evaluates H>0,this would ensure a minimum quality for a cell in the MBMS layer beforeconvergence occurs. In cell reselections, when the FLC is active, the UEselects a cell with the highest R value (the R criterion is defined inTS25.304) on the preferred MBMS layer as long the H criterion (H>0) ismet for the MBMS layer. The cell selection criterion S in 25.304 has tobe met for a cell that the UE selects/reselects based on the FLCcriteria in order to ensure that the UE is camped on a suitable cell. Incase of the initial cell reselection after the FLC has been activatedthe UE may choose a cell reselection initiated by the FLC the UE maydisregard the penalty time and TEMP_OFFSET in order to allow faster onthe preferred MBMS frequency layer convergence. Furthermore, in thefirst cell reselection after the FLC has been activated the UE maychoose a MBMS layer cell that fulfils S and H criterion but it does notnecessarily have the highest R value. In the following cell reselectionthe UE should select a cell, which has the highest R value and fulfillthe S and H criterion. The immediate FLC would provide a shorterconvergence time.

FIGS. 2 and 3 show schematic diagrams of a portion of a network nothaving a hierarchical cell structure. If a network does not use HCS, theoffset used in the R criterion is changed in order to control cellselection for MBMS. The R criterion is defined in TS25.304. That is,Q_(offset) in the R criterion is changed. In FIG. 2, the serving cell isnot on the MBMS layer. In FIG. 3, the serving cell is on the MBMS layer.

The change of offset value for the cells of the MBMS layer could eitherbe done by signaling an additional Qflcoffset t, which is valid for thecells on the MEMS carrier frequency. In case of several MBMS layersQflcoffset should be signaled for each MBMS frequency. This offset(s)would be provided upon notification. The FLC parameters may be sent e.g.in the session control start message on MCCH or via SIB (SystemInformation Block types). Qflcoffset and can be done in 2 ways asdiscussed below

R_(n) for all the neighbour cells on the desired MBMS layer would thenbe calculated as follows:

Serving cell R _(s) =Q _(meas,s) +Qhyst,

Neighbour cells R _(n) =Q _(meas,n) −Qoffset_(s,n)+(F)*Qflcoffset−TO_(n)*(1−L _(n))

Where:

F=1 if the serving cell is not on the preferred MBMS frequency butneighbour cell n is on the MBMS preferred frequency

F=0 if neither the serving cell nor neighbour cell n are on the MBMSpreferred frequency

F=−1 if the serving cell is on the preferred. MBMS frequency butneighbour cell n is not on the MBMS preferred frequency

F=0 if the serving cell and neighbour cell n are on the MBMS preferredfrequency

Another method would be to signal a new offset value that would thenreplace the Qoffset_(s,n) values of all the neighbour cells on thedesired MBMS layer.

The UE would then reselect the cell, that has the highest R value. (TheR criterion and parameters are defined in TS25.304). In the case of theinitial cell reselection initiated by the FLC, the UE may disregard thepenalty time and TEMP_OFFSET in order to allow faster frequency layerconvergence. The cell selection criterion S in 25.304 has to be met fora cell that the UE selects/reselects based on the FLC criteria in orderto ensure that the UE is camped on a suitable cell. In the first cellreselection after the FLC has been activated the UE may choose a MBMSlayer cell on the preferred MBMS frequency layer that fulfils S but itdoes not necessarily have the highest R value. In the following cellreselection the UE should select a cell, which has the highest R valueand fulfill the S and H criterion.

The UE would then reselect the cell with the highest R value. (The Rcriterion and parameters are defined in TS25.304). In the case of theinitial cell reselection initiated by the FLC, the UE may disregard thepenalty time and TEMP_OFFSET in order to allow faster frequency layerconvergence.

Thus, the FLC could occur immediately after the notification and afterthat the UE would follow the new FLC parameters and corresponding cellreselection criteria until the MBMS session ends. After this initialimmediate reselection of MBMS layer, the UE would follow the normal cellreselection criteria with the modified offset value(s) for the MBMSlayer(s).

Alternatively, the new MBMS cell may have to be better ranked than theserving cell during a time interval T_(reselection) before cellreselection occurs. This would cause additional delay to cellreselection but it is reasonable if the value of T_(reselection) is nothigh. The parameter range of T_(reselection) may be set from 0 to 31seconds with a step of 1 second. Alternatively The cell selectioncriterion S in 25.304 has to be met for a cell that the UEselects/reselects based on the FLC criteria in order to ensure that theUE is camped on a suitable cell.

When the MBMS session is finished, the Q_(offset) values would bechanged back to normal.

The FLC parameters and cell reselection rules are valid during the MBMSsession. When the MBMS session ends the UE starts using normal cellreselection parameters and criteria again (i.e. the HCS_PRIO is changedto the normal values given in the system information for normal cellreselection and the Qflcoffset is no longer used in cell reselections).

The above described methods are implemented as follows.

The UTRAN (RNC) sends parameters related to the FLC when it notifies theUE that the MBMS session will start. This may be done e.g. in thesession control start message on MCCH or via SIB (System informationBlock types).

When the FLC is used in the network, the UE has to indicated a sessionstop so that the UE can start using normal cell reselection parametersand criteria again.

The UE reads the FLC parameters when it has been notified that the MBMSsession starts and start using the FLC cell reselection parameters incell reselection (in order to make frequency layer convergencepossible).

When the MBMS session ends the UE reverts back to the normal cellreselection rules.

This invention provides a working FLC method (cell reselection criteria)for MBMS in a network with and without. HCS. The method is backwardscompatible—i.e. can be used with all R99 features, including HCS. R99re-selection rules remain as they are.

Advantages of the HCS case are:

-   -   Simple solution. It works by merely assuming different values of        HCS_PRIO for a certain frequency.    -   If re-selection to the MBMS layer only occurs when H>0, we        ensure t a minimum quality before convergence occurs.

Advantages of the non-HCS case are:

-   -   Simple solution. It works by merely assuming different Qoffset        value for a certain frequency.

Other embodiments of the present invention are also envisaged. Forexample, the present invention may also be utilized in providing othertypes of service in a RAN.

The system is preferably a 3G/UMTS system, or a derivative thereof, butthe present invention could be used in other systems.

There follows a further description of an illustrative example of theinvention.

1. Introduction

The Frequency Layer Convergence (FLC) concept was included to [4] inRAN2#40 introduced based on revised text from [3]. The intention behindthe FLC concept is to maximise the p-t-m connections for an MBMSsession, from the RNC point of view. This is because MBMS in p-t-p wouldnot present many advantages over the R99 DCH connection since the sameradio resources are consumed. It is currently not possible to converge aUE to a certain cell or frequency in the following RRC states: Idle,CELL_FACH, CELL_PCH. Even though included in the [4], The FLCdescription is still at a general level, and requires further refinementbefore stage-3 work can be started. In this contribution, we present aNokia view on the requirements and assumptions related to FLC concept.Based on those, we identify the impact of FLC to some MBMSprocedures/features and propose the changes to be made to various partsof [4] to explicitly describe this impact as well as the underlyingassumptions.

2. Discussion

2.1. FLC assumptions and Requirements

In documents R2-031716, R2-032077 and R2-040086 the FLC concept isdiscussed. However, the text describing FLC in [4] does not capture allthe underlying assumptions. According our view, at least the followingassumptions are valid:

1. Not all MBMS capable UEs should reselect to the MBMS layer.

Only the UEs that have activated the MBMS user service for which asession is starting shall have moved to the MBMS layer. This will avoidall MBMS UEs that have activated other MBMS service reselecting alwaysto the same frequency when any MBMS service is transmitted and minimisethe migration trend of MBMS UEs towards bigger cells although normalcell reselection parameters would prioritise smaller cells e.g. on microlayer.

2. The FLC shall only be active after the reception of notification.

(This implies that MICH and MCCH are present at all cells to deliversession start signalling). It is not stated clearly in [4] whether theUE should move when joining the session or when it is notified. Nokia'spreference the latter one since it allows the FLC to happen only when itis needed i.e. when the session starts. This is important since cellre-selection based on the FLC is not typically indicating the best cellto camp on based on the normal cell reselection rules that are in use inthe network. MICH and MCCH in each cell, counting at target frequency.There needs to be a delay to allow re-selection.

3. There shall be an explicit session stop to indicate disabling theFLC. Since FLC will typically present a less optimum cell re-selection,the time the UE spends actively using this feature should be minimised.

4. FLC-based cell re-selection should only occur on the areas where thepreferred

MBMS frequency layer can provide acceptable quality.

Required limitations: FLC can only occur in cells which overlap incoverage and the adjacent cells must be at the same frequency. It hasrecently been discussed in RAN2 that the FLC should only occur in caseof co-located cells. We have made some further analyses on how to ensuresmooth initial frequency layer convergence and to maintain the UE on thepreferred MBMS layer as long as session is active and the preferred MBMSfrequency layer can provide acceptable quality (i.e. at least the Scriterion is met). We found out that it is rather easy to define whatthe co-location requirement mean in case of initial frequency layerconvergence but it becomes a bit more complicated when the UP startsmaking cell re-selections within the MBMS layer. All cells on the MBMSlayer could potentially be co-located with a cell on another frequency,potentially the one from where the initial FLC was made. It may bepossible to define acceptable FLC cell re-selection rules that fulfilthe requirements set by this document.

There is preferably no attempt to converge UEs towards a specific cell,because this would cause high interference on neighbouring cells.Instead general FLC layer rules, which are valid for all neighbour cellson the MBMS layer, should be defined.

6. FLC shall be backwards compatible—i.e. allow inter-working with theexisting cell reselection criteria

7. FLC shall be available for networks with and without HCS.

8. It is assumed the MBMS layer also provides R99/4/5 servicesindependently of MBMS services—i.e. R99/4/5 UEs may also camp on theMBMS layer cells.

2.2. impact on other MBMS procedures/features

Reasoning:

-   -   1. FLC is only available during MBMS session. (The consequence        of 2 and 3 is that)    -   2. FLC needs to use a cell reselection based method. This means        that the UE will select the best cell, based on a set of        modified rules given by the network. The network is able to        switch this feature ON/OFF, with the start/finish of the MBMS        session.    -   3. Session start procedure needs to be enhanced to take FLC into        account.    -   4. Session stop procedure needs to be used, if FLC is used.    -   5. MICH and MCCH needs to be present also in all cells within        the MBMS service geographical area, even if there is no MTCH.

4. Proposal

It is proposed that the following changes should be agreed to beincluded in the TS. Once there is an agreement, CR can be made, oranother action can be taken.

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6.3. MBMS Notification indicator Channel

MBMS notification utilizes a new MBMS specific PICH called MBMSNotification Indicator Channel (MICH) in cell. MICH frame is presentedin FIG. 7. The exact coding is defined in Stage-3 physical layerspecifications. When FLC is used, MICH channel can be present in a cellindependently of the presence of MTCH channels.

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8.1.1 Session start

Upon receiving a session start indication from CN, UTRAN initiates thesession start sequence to allocate radio resources to UEs for receivingthe MBMS content. As part of this sequence, UTRAN may apply the countingprocedure (counting the number of idle mode UEs) to decide whether touse the p-t-m or p-t-p transfer mode. The FLC may also be activatedduring session start sequence, which may cause cell re-selection duringthe session start sequence. In this case, cell re-selection shall takeplace after MCCH is read.

FIG. 5 shows an example of a possible session start sequence.

In general, the session start sequence involves the following steps:

-   -   In case UTRAN applies counting to determine the most optimal        transfer mode, it may first apply conventional paging to move        UEs in URA_PCH to CELL_PCH state. Next, the following steps are        performed:        -   UTRAN sets the correct MBMS Notification Indicator (NI) and            sends the MBMS ACCESS INFORMATION including service ID, and            access probability on MCCH.        -   Upon DRX wa.keup, UEs in idle mode as well as UEs in            CELL_PCH, URA_PCH and CELL _EACH not receiving an MBMS            service provided in p-t-m transfer mode evaluate the MBMS NI            and if set, read MCCH at the pre-defined time(s). Upon            receiving the MBMS ACCESS INFORMATION including access            probability, UEs in idle mode for which the probability            check passes, initiate RRC connection establishment to move            to PMM CONNECTED. RRC Connected mode UEs ignore the MBMS            ACCESS INFORMATION. UTRAN counts the UEs interested in the            MBMS service using UE linkina from CN        -   In case a pre-defined threshold is reached, UTRAN applies            the p-t-m RB establishment procedure specified below.            Otherwise, UTRAN may repeat the MBMS ACCESS INFORMATION a            number of times, using different probability values. If the            threshold is not reached, UTRAN applies the p-t-p RB            establishment procedure    -   NOTE: The NIs are evaluated by UEs in CELL_PCH, URA_PCH and        CELL_FACH that are not receiving an MBMS service that is        provided using p-t-m transfer mode. In this section these UEs        are referred to as ‘NI-detecting connected mode UEs’. The UEs in        CELL_PCH, URA_PCH, CELL_FACH and CELL_DCH that are receiving an        MBMS service that is provided using p-t-m transfer mode receive        the Secondary Notification Indicator (SNI) instead. The latter        UEs are referred to as ‘SNI detecting connected mode UEs’.    -   In case UTRAN selects the p-t-m RB establishment procedure:        -   UTRAN configures MTCH and updates MCCH (MBMS SERVICE            INFORMATION and MBMS RADIO BEARER INFORMATION) by including            the service ID and p-t-m RB information for the concerned            MBMS service        -   In case p-t-m RB establishment is not preceded by counting,            UTRAN sets the correct MBMS Notification Indicator (NI).            Regardless of counting, UTRAN also provides the Secondary            Notification Indicator.        -   UTRAN sends the MBMS dedicated notification message            including the service ID and cause=session start on DCCH to            inform UEs in CELL_PCH that are not receiving art MBMS            service provided using p-t-m transfer mode        -   In case p-t-m RB establishment is preceded by counting, UEs            in idle mode as well as NI-detecting connected mode UEs read            MCCH at the pre-defined time(s) to acquire the MBMS SERVICE            INFORMATION and MBMS RADIO BEARER INFORMATION        -   In case p-t-m RB establishment is not preceded by counting,            Upon DRX wakeup, UEs in idle mode as well as NI-detecting            connected mode UEs evaluate the MBMS NI and if set, read            MCCH at the pre-defined time(s)to acquire the MBMS SERVICE            INFORMATION and MBMS RADIO BEARER INFORMATION        -   Upon detecting the MBMS SNI, SNI-detecting connected mode            UEs read MCCH at the pre-defined time(s) to acquire the MBMS            SERVICE INFORMATION and MBMS RADIO BEARER INFORMATION. UEs            that are incapable of receiving the MTCH for the session            that is started in parallel to the existing activity notify            the user. This enables the user to choose between the            ongoing activity and the new MBMS service        -   Upon receiving MBMS dedicated notification with            cause=session start, UEs in CELL_DCH that are incapable of            receiving the MCCH and the corresponding MTCH in parallel to            the existing activity notify the user. This enables the user            to choose between the ongoing activity and the new MBMS            service. If the user decides to receive the new MBMS            service, the UE shall read MCCH at the pre-defined time(s)            to acquire the MBMS SERVICE INFORMATION and MBMS RADIO            BEARER INFORMATION.        -   Upon receiving the MBMS SERVICE INFORMATION and the MBMS RB            INFORMATION including the p-t-m RB information for the            concerned MBMS service, the UE starts receiving the p-t-m            radio bearers    -   In case UTRAN selects the p-t-p RB establishment procedure:        -   UTRAN applies conventional paging to trigger UEs in CELL_PCH            to perform cell update. Furthermore, UTRAN establishes the            p-t-p RB by means of appropriate RRC procedures eg. the RB            setup procedure        -   UEs establish the p-t-p radio bearers by means of the RRC            procedure selected by UTRAN eg. the RB setup procedure        -   UTRAN updates MCCH (MBMS SERVICE INFO) to inform UEs joining            or entering the cell at a later point in time.

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8.1.4 Session stop

UTRAN may apply the session stop procedure to inform UEs that the end ofMTCH transmission concerns the end of a session rather than just an idleperiod. The purpose of the procedure is to reduce the UE powerconsumption and to allow the UE to disable the frequency layerconvergence functionalities when there are no ongoing MEMS sessionsrequiring the use of FLC. When FLC is applied UTRAN shall apply sessionstop procedure.

FIG. 6 shows an example of a possible session stop sequence.

In case UTRAN provides the service p-t-m, the session stop sequenceinvolves the following steps:

-   -   UTRAN sets the correct MBMS NI and provides the SNI    -   Upon DRX wakeup, UEs in idle mode as well as NI detecting        connected mode UEsevaluate the MBMS NI and if set, read MCCH at        the pre-defined time(s) to acquire the required MCCH        information. Upon receiving this information the UE stops        receiving the MTCH    -   Upon detecting the MBMS SNI, SNI-detecting connected mode UEs        read MCCH at the pre-defined time(s) to acquire the required        MCCH information. Upon receiving this information the UE stops        receiving the MTCH

In case UTRAN provides the service p-t-p, the session stop sequenceinvolves the following steps:

-   -   UTRAN releases the p-t-p radio hearers and updates MCCH (MBMS        SERVICE INFO) to inform UEs joining or entering the cell at a        later point in time.

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11.2 Frequency layer Convergence

Frequency Layer Convergence denotes the process where the UTRAN requestsUEs to preferentially re-select to the frequency layer on which the MBMSservice is intended to be transmitted. This layer preference could bedone by an additional MBMS session related Layer Convergence Information(LCI) such as offset and target frequency. These kinds of informationcould be given to UEs at session start and during the whole session, andwill be applied during the entire session. More than one offset may berequired to support multiple frequencies, but it is assumed that thesame LCI information will apply to all the services on the samefrequencies. The details of the mechanism are defined in state 3, butthe mechanism should fulfil the following requirements:

-   -   Not all MBMS capable UEs should reselect to the MBMS layer.    -   The FLC shall only be active after the reception of        notification.    -   There shall be an explicit session stop to indicate disabling        the FLC.    -   FLC-based cell re-selection should only occur on the areas where        the preferred MBMS frequency layer can provide acceptable        quality    -   FLC shall be backwards compatible—i.e. allow inter-working with        the existing cell reselection criteria    -   FLC shall be available for networks with and without HCS.    -   It is assumed the MBMS layer also provides R99/4/5 services        independently of MBMS services—i.e. R99/4/5 IJEs may also camp        on the MBMS layer cells.

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REFERENCES

[1] R2-031716

[2] R2-032077

[3] R3-040086

[4] 25.346 v.6.0.0

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole in the lightof the common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein, and without limitation to the scope ofthe claims. The applicant indicates that aspects of the presentinvention may consist of any such individual feature or combination offeatures. In view of the foregoing description it will be evident to aperson skilled in the art that various modifications may be made withinthe scope of the invention.

1. A method to control cell selection and/or re-selection in acommunication system comprising a plurality of cells with which terminaldevices may communicate, the method comprising: determining that aterminal device is to start a session for a multimedia broadcastmulticast service (MBMS), the multimedia broadcast multicast serviceusing a preferred frequency layer; and changing, based on thedetermination that the terminal device is to start the session, a cellselection priority parameters of a cell in the plurality of cells usingthe preferred frequency layer for the MBMS from normal values, the cellselection priority parameter being for prioritizing the cell in theplurality of cells to be selected or reselected for the terminal device.wherein changing the cell selection priority parameters comprises atleast one of at least triggering immediate selection or reselection ofthe cell and making selection or reselection more likely for the cell.2. The method of claim 1, further comprising selecting which of aplurality of cell selection or reselection parameters is to be changedbased on the cell selection priority parameter.
 3. The method of claim1, wherein changing the cell selection priority parameter comprisesreceiving data identifying a new value for the cell selection priorityparameter from the MBMS.
 4. The method of claim 3, wherein the data isreceived by means of a unicast session control start message or by meansof a broadcast system information data message.
 5. The method of claim1, wherein changing the cell selection priority parameter comprisessetting a parameter that reduces the responsiveness of the terminaldevice to high mobility triggers.
 6. A terminal device comprising: aprocessor; a memory coupled to the processor, the memory configured tostore computer program code that, when executed by the processor, causethe terminal device to: determine that a terminal device is to start asession for a multimedia broadcast multicast service (MBMS), themultimedia broadcast multicast service using a preferred frequencylayer; and change, based on the determination that the terminal deviceis to start the session, a cell selection priority parameter of a cellin the plurality of cells using the preferred frequency layer for theMBMS from normal values, the cell selection priority parameter being forprioritizing the cell in the plurality of cells to be selected orreselected for the terminal device, wherein changing the cell selectionpriority parameter comprises at least one of at least triggeringimmediate selection or reselection of the cell and making selection orreselection more likely for the cell.
 7. The terminal device of claim 6,wherein the terminal is further caused to select which of a plurality ofcell selection or reselection parameters is to be changed based on thecell selection priority parameter.
 8. The terminal device of claim 6,wherein changing the cell selection priority parameter comprisesreceiving data identifying a new value for the cell selection priorityparameter from the MBMS.
 9. The terminal device of claim 8, wherein theterminal device is configured to receive the data by one of a unicastsession control start message and a broadcast system information datamessage.
 10. The terminal device of claim 6, wherein the terminal isfurther caused to change the cell selection priority parameter bysetting a parameter that reduces the responsiveness of the terminaldevice to high mobility triggers.
 11. A non-transitory computer-readablememory adapted for use by a terminal device in requesting and using amultimedia broadcast multicast service, the non-transitorycomputer-readable memory used to direct the terminal device to performthe steps of: determining that a terminal device is to start a sessionfor a multimedia broadcast multicast service (MBMS), the multimediabroadcast multicast service using a preferred frequency layer; andchanging, based on the determination that the terminal device is tostart the session, a cell selection priority parameter of a cell in theplurality of cells using the preferred frequency layer for the MBMS fromnormal values, the cell selection priority parameter being forprioritizing the cell in the plurality of cells to be selected orreselected for the terminal device, wherein changing the cell selectionpriority parameter comprises at least one of at least triggeringimmediate selection or reselection of the cell and making selection orreselection more likely for the cell.
 12. The non-transitorycomputer-readable memory of claim 11, further comprising selecting whichof a plurality of cell selection or reselection parameters is to bechanged based on the cell selection priority parameter.
 13. Thenon-transitory computer-readable memory of claim 11, wherein changingthe cell selection priority parameter comprises receiving dataidentifying a new value for the cell selection priority parameter fromthe MBMS.
 14. The non-transitory computer-readable memory of claim 13,wherein the data is received by means of a unicast session control startmessage or by means of a broadcast system information data message. 15.The non-transitory computer-readable memory of claim 11, whereinchanging the cell selection priority parameter comprises setting aparameter that reduces the responsiveness of the terminal device to highmobility triggers.